We use nginx as load balancer and reverse proxy for some static content (images etc).
And a problem was found with enabling SPDY: cached content with enabled SPDY becomes get from server with greater request time and i think slower (according Chrome debug console).

Here is a graphical illustration of problem: in the middle for some time was enabled spdy, but not other time on both sides.
It shows average $request_time and $upstream_response_time variables sum every second: sum(time)/sum(requestcount) per second